Critical electrical cable and wiring systems in aging aircraft, ships, nuclear power plants, and industrial complexes are a growing concern due to risk of failure from prolonged environmental stresses, such as thermal and mechanical cycling, and electrical stress. Such applications have mission or safety critical cable infrastructures that must function without fault during normal operations and possibly during an abnormal event.
Examples of safety critical electrical cabling in commercial and military aircraft are the flight control systems. During operations, aircraft environments include vibration and thermal variations, which can result in an accumulation of damage to a cable. It is critical that the damaged cable be identified and replaced or repaired. If the defect is left undetected, the environmental degradation will continue, and the accumulated damage could eventually result in a critical fault if not corrected.
An example of environment stress in the nuclear power industry is thermal embrittlement that can result in cracking of insulation in control cables. The damaged cable may never fail under normal operation. However, during an earthquake the shifting of cables in a tray and breaking away of the embrittled insulation could result in an immediate failure. Depending on the critical nature of the cable, it may not be necessary to immediately replace the damaged cable. With the low probability of a failure scenario, cable replacement could occur during normal maintenance operation. If facility operators knew the condition of the cables and the location of the defects, they could make informed decisions on repair methodologies.
In general, these critical electrical cable systems are inaccessible over their length, providing very limited visual or physical inspection of the system. Nondestructive and nonintrusive condition monitoring (CM) techniques are needed to locate insulation degradation and defects in such inaccessible cable systems.
Despite the compelling need for CM tools to evaluate the reliability of critical cable systems, validated CM technologies have not been developed because of the complexity of the problem. A variety of commercial and exploratory tools are available that provide information on bulk cable properties, but no validated CM technique is available for locating insulation degradations in complex cable systems. One technique that has been proposed is partial discharge. The partial discharge technique, however, has not been demonstrated to function outside of highly controlled laboratory environments. Other CM techniques that have been proposed, and in some cases implemented, use continuous application of high voltage and immersion of the wiring or cable system in water or ionizing gas to enhance the possibility of electrical breakdown at defect sites. However, these techniques have limited applicability because of the requirement for water or gas immersion. Nor have these techniques been demonstrated to be non-damaging to the cables under test.
The present invention, hereinafter referred to as Pulsed-Arrested Spark Discharge (PASD), is potentially capable of in-situ, nondestructive detection and location of insulation defects in complex cable systems. The PASD method has possible utility in any operation that has electrical cable systems that must be evaluated to determine the presence of defects or degradations.